Electrochemical cell and method of fabricating same

ABSTRACT

An electrochemical cell having a cell package made of a metallic material to allow the cell package to be sealed by welding, even when contaminated, and a method of manufacturing the electrochemical cell. The method of fabricating the cell, includes the steps of forming an electrode cell stack and a metallic cell package having a base portion and a lid portion which are welded to each other to define an enclosure, the cell package including a first section for receiving the cell stack and a second section having an inlet port which communicates with the first section; placing the cell stack into the enclosure in the first section; sealing the lid portion to the base portion around a periphery of the cell package to form a peripheral seam; applying a vacuum to the enclosure through the inlet port in the cell package; introducing an electrolyte into the enclosure via the inlet port; and welding the lid portion to the base portion to form a first weld seam located between the first and second sections to seal off the first section from the second section. The first weld seam extends from the peripheral seam on a first side of the cell package to the peripheral seam a second side of the cell package. The method further includes the steps of puncturing the cell package to form an evacuation port located in a third section of the cell; partially charging the cell stack resulting in generation of gases inside the enclosure; applying a vacuum to the evacuation port of the cell stack to withdraw the gases; and sealing the lid portion to the base portion across a second weld seam located between the first section and the third section.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an improved cell package whichcan be welded to hermetically seal the cell package after the cell stackand electrolyte have been placed in the package and a method ofmanufacturing the same.

[0003] 2. Background

[0004] A important consideration in the manufacturing of electrochemicalbatteries is the manner in which the electrolyte is introduced into thecell stack. As discussed in a related patent application, one currenttechnique includes the steps of pouring the electrolyte into the cellstack during the manufacturing of the cell stack in a machine, placingthe electrolyte impregnated cell stack into the cell package, evacuatingthe cell package and heat sealing the package.

[0005] This technique has shortcomings. One potential concern is theloss of electrolyte during the step of pouring the electrolyte into thecell stack and the subsequent step of evacuating the package. Theelectrolyte is a relatively expensive component of the electrochemicalcell. Thus, the loss of electrolyte increases the overall cost ofmanufacturing the cell.

[0006] A second potential concern is that the electrolyte that issuctioned from the cell stack during the evacuating step contaminatesthe inside of the package. Such contamination of the package may make itdifficult to securely seal the package. As such, subsequent leakage ofthe electrolyte from the sealed package may result. A further concern isthat the pouring step must be performed in a glove box environment(i.e., dry and inert atmosphere). Since this step is an intermediatestep in the manufacturing of the cell stack, the machine whichmanufactures the cell stack must consequently have a glove boxenvironment, thus driving up the cost of the machine. In addition, whenthe electrolyte is poured into the cell stack, the electrolytecontaminates the machine.

[0007] The current cell package is formed of a laminate of a polyesterouter layer, an aluminum barrier layer and a polyethylene orpolypropylene inner layer. The polyester layer provides strength, thealuminum layer prevents water from penetrating the cell package and theinner layer allows for the heat sealing of the cell package.Specifically, generally, the cell package includes two parts that arebonded together around their periphery by heat sealing the inner layersto each other. The problem with this laminate is that once contaminatedwith electrolyte, the inner layers may not form a secure heat seal. Thismakes degassing and resealing of the cell package a problem. Finally,when a polymer is used as an inner layer, the electrolyte may still beable to permeate through the polymer itself. This is especially true ifthe battery is exposed to elevated temperatures.

SUMMARY OF THE INVENTION

[0008] It is an object of the invention to provide a method ofmanufacturing an electrochemical cell which overcomes the aboveproblems. In particular, an object of the invention is to provide amethod of manufacturing a cell where the electrolyte is introduced intothe cell stack with minimal or no loss of electrolyte. Another object ofthe invention is to provide a method in which the electrolyte fillingstep is performed after the cell stack is manufactured so that the cellstack manufacturing machine does not have to maintain a glove boxenvironment and contamination of the machine is eliminated. Anotherobject of the invention is to provide a packaging, which minimizes thepossibility of electrolyte permeation through the seals.

[0009] These and other objects are achieved by a method of fabricatingan electrochemical cell, comprising the steps of forming an electrodecell stack and a metallic cell package having a base portion and a lidportion which are welded to each other to define an enclosure, the cellpackage including a first section for receiving the cell stack and asecond section having an inlet port which communicates with the firstsection; placing the cell stack into the enclosure in the first section;sealing the lid portion to the base portion around a periphery of thecell package to form a peripheral seam; applying a vacuum to theenclosure through the inlet port in the cell package; introducing anelectrolyte into the enclosure via the inlet port; and welding the lidportion to the base portion to form a first weld seam located betweenthe first and second sections to seal off the first section from thesecond section. The first weld seam extends from the peripheral seam ona first side of the cell package to the peripheral seam a second side ofthe cell package.

[0010] The method further includes the steps of partially charging thecell stack resulting in generation of gases inside the enclosure;puncturing the cell package to form an evacuation port located in athird section of the cell; applying a vacuum to the evacuation port ofthe cell stack to withdraw the gases; and sealing the lid portion to thebase portion across a second weld seam located between the first sectionand the third section. According to one preferred aspect of theinvention the second weld seam extends from the first side to a thirdside opposite the first side. After the second weld seam has beenformed, the excess portions of the cell package, corresponding to thesecond and third sections, are removed from the first section whichholds the cell stack.

[0011] The electrochemical cell according to a preferred embodiment ofthe invention comprises: a casing; and an electrode cell stack containedwithin the casing along with an electrolyte. The casing includes a baseand a lid that are made of a metallic material such that they can bewelded to each other along a seam weld to form an enclosure forreceiving the cell stack. This is different from conventional cellpackages where the parts are heat sealed to each other. The metallicmaterial of the casing is, for example, aluminum, copper, nickel orstainless steel. The weld seam extends around a periphery of the cellpackage.

[0012] The cell stack includes first and second tabs of oppositepolarity. The electrochemical cell further comprises a pass-throughterminal secured to the casing and electrically connected to the secondtab while the first tab is electrically connected to the casing.According to one aspect of the invention, the pass-through terminalcomprises an eyelet having a first through-hole, an insulator located inthe first through-hole of the eyelet and having a second through-hole;and a terminal post located in the second through-hole of the insulatorso as to be insulated from the eyelet, wherein the eyelet is welded tothe metallic material of the casing and the terminal post iselectrically connected to the second tab of the cell stack. If thecasing is made of copper, the eyelet is nickel plated iron, theinsulator is glass and the terminal post is molybdenum. Also, theterminal post and the second tab have a positive polarity and the firstterminal and the copper casing have a negative polarity.

[0013] On the other hand, when the casing is made of aluminum, theeyelet is aluminum, the insulator is ceramic and the terminal post iscopper. In this case the terminal post and the second tab have anegative polarity and the first terminal and the aluminum casing have apositive polarity.

[0014] According to another aspect of the invention, when the casing isaluminum, the pass-through terminal comprises a copper rivet, at leastone insulator circumscribing the rivet so as to insulate the rivet fromthe casing, and a nickel washer disposed on an outside of the casing andcontacting the rivet with the insulator insulating the washer from thecasing. In this case, the rivet and the second tab have a negativepolarity and the first terminal and the aluminum casing have a positivepolarity.

[0015] With the above electrochemical cell and related fabricationtechnique there is little or no electrolyte loss. In particular, sincethe electrolyte is injected into the electrode cell stack after thepackage has been sealed, substantially all of the electrolyte issuctioned into the electrode cell stack without any of the electrolyteescaping from the package. In addition, contamination of the cellmanufacturing machine with electrolyte is minimized. Accordingly, all ofthe concerns discussed above with respect to the current technique areovercome.

[0016] Further, since the casing is made of a metallic material such ascopper or aluminum, the package can be sealed by welding, instead of byheating. It has been discovered that electrolyte contamination does notinterfere with a welded seal. The welding process can be, but is notlimited to, ultrasonic welding.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and advantages of thepresent invention will be better understood from the followingspecification when read in conjunction with the accompanying drawings inwhich:

[0018]FIG. 1 is a plan view showing the cell package with the cell stacklocated therein;

[0019]FIG. 2 is a sectional view taken along line 2-2 of FIG. 1 showingthe cell package;

[0020]FIG. 3 is a sectional view showing the pass-through terminal ofthe present invention for interconnecting one of the tabs of the cellstack to an external equipment, according to one aspect of theinvention;

[0021]FIG. 4 is a sectional view showing the pass-through terminal ofthe present invention for interconnecting one of the tabs of the cellstack to an external equipment, according to another aspect of theinvention;

[0022]FIG. 5 is a plan view showing the cell package after theelectrolyte has been introduced into the cell package;

[0023]FIG. 6 is a sectional view taken along lines 6-6 of FIG. 5;

[0024]FIG. 7 is a plan view of the cell package after the degassingstep;

[0025]FIG. 8 is a sectional view taken along line 8-8 of FIG. 7;

[0026]FIG. 9 is a plan view of the cell package after the removal of theexcess material of the cell package; and

[0027]FIG. 10 is a sectional view taken along line 10-10 of FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Referring to FIGS. 1 and 2, the electrochemical cell 8 includes acell package 10 having the shape of an envelope which is formed of ametallic sheet or sheets 12 so as to define an opening 14 therein forreceiving a cell stack 16. The package is preferably formed of twometallic sheets 12 that are welded along the edge to form weld seam 18.The welding process can be, but is not limited to, ultrasonic welding.

[0029] One of the two sheets is a base 19 that has a cell stack cup 20in which the cell stack 16 is placed. The other sheet is a lid 21.Alternatively, the package 10 can be formed from a single metallic sheetthat is folded in half leaving only three edges to be welded. Accordingto the preferred embodiment, the metal sheet is made from aluminum orcopper, although the invention is not to be limited to these materials.For example, other suitable materials include stainless steel andnickel.

[0030] As is conventional, the cell stack 16 includes a first tab 22 (ofa first polarity) and a second tab 24 (of a second polarity). Since thecell package 10 is made of a metallic material which is conductive,according to the invention, the first tab 22 of the cell stack 16 iselectrically connected directly to the cell package at weld 23. On theother hand, the second tab 24 is connected to a pass-through terminalassembly 26 (shown schematically in FIGS. 1 and 2) which is provided inone of the sheets of the cell package to allow external connection tothe second tab 24 of the cell stack. As discussed below, the polarity ofthe first and second tabs is dependent on the material of the cellpackage.

[0031] Referring to FIG. 1, the cell package also includes anelectrolyte introducing portion 28 and degassing portion 30 whichcommunicate with the inside of the package. Each of these portionsincludes a washer 29 which is welded to the inside surface of the cellpackage material, as shown in FIGS. 2 and 8. As discussed in greaterdetail below, the electrolyte introducing portion 28 has an electrolyteport 31 therein. The port 31 can be formed before or after the cellpackage is formed. On the other hand, as discussed below, the degassingportion 30 is punctured after the cell stack formation process to formdegassing port 33 therein. The electrolyte port 31 is used to introducethe electrolyte into the cell package 10 to activate the cell stack 16and the degassing port 33 is used to degas the cell package 10 afterformation. The material of the washer 29 must be compatible with that ofthe cell package. If the cell package 10 is made of copper, it ispreferable that the washer 29 be nickel plated iron; if the cell package10 is made of aluminum, it is preferable that the washer be aluminum.

[0032] The following is a description of the design of the pass throughterminal assembly 26. There are two alternative designs respectivelyillustrated in detail in FIGS. 3 and 4. With reference to FIG. 3,according to a first of these designs, the pass-through terminalassembly 26 includes an eyelet 32, an insulator 34 and a terminal post36. The eyelet 32 and insulator 34 are tubular members. The insulator 34is located inside the eyelet 32 and the terminal post 36 is locatedinside the insulator 34. The cell package 10 has a hole 38 thereinthrough which the terminal post 36 protrudes. The eyelet 32 is locatedon the inside of the cell package 10 with the back surface 40 of theeyelet welded to the inside surface 42 of the cell package. A plasticwasher 44 is adhered to the outside surface 46 of the cell package.

[0033] Referring also to FIG. 1, the second tab 24 is electricallyconnected to the terminal post 36 of the terminal assembly 36 via a lead48 which is welded at one end to the second tab 24 and at the other endto the terminal post 36. Thus, with this arrangement, the second tab 24is electrically connected to the terminal post 36, which protrudes tothe exterior of the cell package 10, while being insulated from themetallic cell package by the insulator 34. Hence, when connecting thecell to the external equipment, one terminal (not shown) of theequipment is simply placed in contact with the metallic cell package 10to which the first tab 22 of the cell stack is connected, and the otherterminal (not shown) of the external equipment is electrically connectedto the terminal post 36, to which the second tab 24 of the cell stack iselectrically connected via lead 48.

[0034] The lead 48 and the accessible parts of the stack 16, with theopposite polarity of the metallic packaging 10, should be insulatedusing internal insulators 80 and 81, as shown in FIGS. 5 and 6.

[0035] As noted above, according to the preferred embodiment of theinvention, the cell package can be made of either aluminum or copper.While nickel is also an option, it is relatively expensive and, hence,not preferred. When the cell package is made of copper, the first tab 22of the cell stack 16 has a negative polarity and the second tab 24 ofthe cell stack 16 has a positive polarity. Therefore, in this case thecell package 10, to which the first tab 22 is directly connected, has anegative polarity and the terminal post 36 of the terminal assembly 26has a positive polarity. Also, it has been discovered that for bestresults, for a cell package made of a copper material, the eyelet 32should be made of nickel plated iron, the insulator 34 should be made ofa glass (e.g., Sandia TR 23™) and the terminal post should be made ofmolybdenum.

[0036] On the other hand, when the cell package 10 is made of aluminum,the first tab 22 of the cell stack 16 has a positive polarity and thesecond tab 24 of the cell stack 16 has a negative polarity. Therefore,in this case the cell package 10, to which the first tab 22 is directlyconnected, has a positive polarity and the terminal post 36 of theterminal assembly 26 has a negative polarity. It is preferable that theeyelet 32 be made of aluminum, the insulator 34 be made of a ceramic(e.g., Al₂O₃) and the terminal post be made of copper.

[0037] An alternative design of the pass-through terminal assembly 26 isillustrated in FIG. 4. This design is preferred when using a cellpackage made of aluminum. According to this embodiment, the terminalassembly 26 includes a rivet 50, an internal washer 52, insulators 54and an external washer 56. According to a preferred embodiment, therivet 50 is made of copper, the internal washer 52 is made of aluminum,the insulators 54 are made of polyethermide (e.g., Ultem™ made byGeneral Electric) and the external washer 56 is made of nickel.

[0038] As shown in FIG. 4, the rivet 50 extends through the holesprovided in the cell package 10, the insulators 54, and the internal andexternal washers 52 and 56 so that it protrudes from the cell package.With the head 58 of the rivet located on the inside of the cell package10, the opposite end 59 of the rivet 50 is flared outwardly until itcontacts the nickel washer 56. The insulators 54 prevent the rivet 50and the external nickel washer 56 from contacting the aluminum cellpackage 10 to prevent shorting of the cell stack 16. The outside face 60of the internal washer 52 is welded to the inside surface 42 of thealuminum cell package such that the terminal assembly 26 is securelyretained to the cell package. The purpose of the external nickel washer56 is to make electrical contact with the negative terminal of theexternal equipment. As with the embodiment of FIG. 2, the second tab 24of the cell stack 16 is electrically connected to the rivet via the lead48. Since the cell package in this embodiment is aluminum, the polarityof the second tab 44 is negative so that the polarity of the rivet 50 islikewise negative. Naturally, the lead 40 must be insulated to somedegree so that it will not contact the cell package which has theopposite polarity.

[0039] A description of the method of activating the cell stack will nowbe provided with reference to the figures. As noted above, FIGS. 1 and 2show the cell stack 16 located inside the cup 20 of the cell package 10.After the cell stack has been placed in the cup 20, the lid 21 is weldedto the base 19 around the periphery of the cell package 10 as indicatedby the weld seam 18. After the cell package has been welded, a vacuum isapplied to the electrolyte port 31 after which electrolyte is introducedthrough the electrolyte port into the cell package 10. After the fillingof the electrolyte, the cell package is welded along weld seam 62, asshown in FIGS. 5 and 6. The electrochemical cell is then partiallycharged (i.e., formation) generating gases inside the cell package 10.As shown in FIGS. 7 and 8, after formation, the degassing portion 30 isthen punctured to form the degassing port 33 in the cell packagingmaterial and a vacuum is then applied to withdraw the formation gasesfrom the inside of the cell package 10. The cell package is then weldedalong weld seam 64 shown in FIG. 7. Referring also to FIGS. 9 and 10,the excess material 66 of the cell package is then trimmed leaving onlythe lower portion 68 where the cell stack 16 is located resulting in theelectrochemical cell 8.

[0040] Having described the invention with particular reference to thepreferred embodiments, it will be obvious to those skilled in the art towhich the invention pertains after understanding the invention, thatvarious modifications and changes may be made therein without departingfrom the spirit and scope of the invention as defined by the claimsappended hereto.

What is claimed is:
 1. A method of fabricating an electrochemical cell,comprising the following steps: forming an electrode cell stack and ametallic cell package having a base portion and a lid portion definingan enclosure, said cell package including a first section for receivingsaid cell stack and a second section having an inlet port whichcommunicates with said first section; placing said cell stack into saidenclosure in said first section; sealing said lid portion to said baseportion around a periphery of said cell package to form a peripheralseam; introducing an electrolyte into said enclosure via said inletport; and welding said lid portion to said base portion to form a firstweld seam located between said first and second sections to seal offsaid first section from said second section.
 2. The method offabricating an electrochemical cell according to claim 1, wherein saidsealing step includes the step of welding said lid portion to said baseportion.
 3. The method of fabricating an electrochemical cell accordingto claim 2, wherein said first weld seam extends from said peripheralseam on a first side of said cell package to said peripheral seam asecond side of said cell package.
 4. The method of fabricating anelectrochemical cell according to claim 3, wherein said first and secondsides are contiguous with each other.
 5. The method of fabricating anelectrochemical cell according to claim 3, further comprising thefollowing steps: at least partially charging said cell stack resultingin generation of gases inside said enclosure; puncturing said cellpackage to form an evacuation port located in a third section of saidcell; applying a vacuum to said evacuation port of said cell stack towithdraw said gases; and welding said lid portion to said base portionacross a second weld seam located between said first section and saidthird section.
 6. The method of fabricating an electrochemical cellaccording to claim 5, wherein said second weld seam extends from saidfirst side to a third side opposite said first side.
 7. The method offabricating an electrochemical cell according to claim 6, furthercomprising the step of cutting said cell package to remove said secondand third sections from said first section.
 8. The method of fabricatingan electrochemical cell according to claim 1, further comprising thestep of applying a vacuum to said enclosure through said inlet port insaid cell package prior to said introducing step.
 9. An electrochemicalcell comprising: a casing; and an electrode cell stack contained withinsaid casing along with an electrolyte, wherein said casing includesfirst and second sheets made of a metallic material, said first andsecond sheets being welded to each other along a weld seam to form anenclosure surrounding said cell stack.
 10. The electrochemical cell ofclaim 9, wherein said metallic material is selected from a groupconsisting of aluminum, copper, nickel and stainless steel.
 11. Theelectrochemical cell of claim 10, wherein said first part is a base andsaid second part is a lid.
 12. The electrochemical cell of claim 11,wherein said weld seam extends around a periphery of said cell package.13. The electrochemical cell of claim 12, wherein said base has a cupfor receiving said cell stack.
 14. The electrochemical cell of claim 12,wherein said cell stack includes first and second tabs of oppositepolarity and wherein said electrochemical cell further comprises: apass-through terminal secured to said casing and electrically connectedto said second tab, said first tab being electrically connected to saidcasing.
 15. The electrochemical cell of claim 14, wherein saidpass-through terminal comprises: an eyelet having a first through-hole;an insulator located in said first through-hole of said eyelet andhaving a second through-hole; and a terminal post located in said secondthrough-hole of said insulator so as to be insulated from said eyelet,wherein said eyelet is welded to said metallic material of said casingand said terminal post is electrically connected to said second tab ofsaid cell stack.
 16. The electrochemical cell of claim 15, wherein saidmetallic material is copper, said eyelet is nickel plated iron, saidinsulator is glass and said terminal post is aluminum.
 17. Theelectrochemical cell of claim 16, wherein said terminal post and saidsecond tab have a positive polarity and said first terminal and saidcopper casing have a negative polarity.
 18. The electrochemical cell ofclaim 15, wherein said metallic material is aluminum, said eyelet isaluminum, said insulator is ceramic and said terminal post is copper.19. The electrochemical cell of claim 18, wherein said terminal post andsaid second tab have a negative polarity and said first terminal andsaid aluminum casing have a positive polarity.
 20. The electrochemicalcell of claim 14, wherein said pass-through terminal comprises a rivet.21. The electrochemical cell of claim 20, wherein casing is aluminum andsaid rivet is copper.
 22. The electrochemical cell of claim 21, whereinsaid pass-through terminal further comprises at least one insulatorcircumscribing said rivet so as to insulate said rivet from said casing.23. The electrochemical cell of claim 22, wherein said pass-throughterminal further comprises a nickel washer disposed on an outside ofsaid casing with said at least one insulator insulating said washer fromsaid casing, wherein said rivet contacts said washer.
 24. Theelectrochemical cell of claim 23, wherein said rivet and said second tabhave a negative polarity and said first tab and said aluminum casinghave a positive polarity.
 25. The electrochemical cell of claim 9, wheresaid first and second sheets are unitary with each other.
 26. A casingfor an electrochemical cell, comprising a metallic layer which is weldedtogether to define an enclosure in which a cell stack can be located.